Wave movements in the sea and in large inland lakes constitutes a potential source that have scarcely been exploited so far. However various suggestions have been made to use the vertical movements of the sea for producing electrical power in a generator. Since a point on the sea surface makes a reciprocating vertical movement it is suitable to use a linear generator to produce the electric power.
WO 2004/085842 discloses such a wave-power unit where the moving part of the generator, i.e. the part that corresponds to the rotor in a rotating generator and in the present application called translator, reciprocates in relation to the stator of the generator. In that disclosure the stator is anchored in the sea bed. The translator is by wire, cable or a chain connected to a body floating on the sea.
It is important that the guiding of linear motion of the translator in relation to the stator is exact and reliable so that the size of the gap between the translator and stator is retained at an exact value. The gap is in the size of 1-5 mm, preferably about 2 mm. Since a generator of the type in question may be fairly large, insufficient precision in the guiding entails that the size of the gap risks deviating substantially from the predetermined one. This entails asymmetry of the occurring magnetic forces, which results in harmful asymmetric forces on the translator with the risk of operational disturbances as well as breakdown. Also the electromagnetic transformation of energy is effected negatively by erroneous gap size.
Between the translator and the stator there are very strong magnetic attraction forces. In order to minimize the load on the bearings therefore the generator preferably is made symmetrical such that the magnet force across the gap on one side outbalances the magnet forces across the gap on an opposite side. The journaling force required thereby is ideally zero.
However when there occurs a slight deviation from the equilibrium the magnet forces on the side where the gap decreases will increase and on the opposite side where the gap increases the magnet forces will decrease. Thereby a resultant magnetic force will act to further move the translator towards the side where the gap is decreased.
The object of the present invention is to arrange the journaling of the translator such that the above described effect that occurs when the gap width changes is counter-acted in an effective way.